County Plans to Start Devil’s Gate Dam Annual Sediment Removal Maintenance Work Monday

Starting Monday, Aug. 14, the Los Angeles County Department of Public Works will begin its second year of annual maintenance at the Devil’s Gate Dam, a vital flood control structure in Pasadena that protects downstream communities from the Arroyo Seco Watershed.

Maintenance work will include clearing vegetation and excavating excess sediment that has accumulated in the reservoir during the past storm season. The sediment removal project aims to restore the dam’s capacity to regulate high runoff flows and prevent flooding.

Constructed in 1920, Devil’s Gate Dam is the oldest dam in the county. 

Over the years, it has filled up with dirt, rocks, trees, and trash, reducing its effectiveness and posing a risk to public safety. It was only when the accumulation reached emergency levels that communities impacted in Los Angeles decided on a massive effort to clear the dam. 

The county launched a four-year campaign in 2018 to remove 1.7 million cubic yards of sediment from the reservoir,  employing hundreds of dump trucks in extensive 14- to 15-hour daily shifts over seven days a week to address the issue. 

As planned, the county Public Works Department will maintain nearly 42 acres within the reservoir in the late summer annually by removing accumulated vegetation and sediment in the basin and repairing erosion caused by the storm season. 

The annual maintenance will allow enhanced native habitat areas to co-exist with reservoir flood control operations and maintenance for the long-term health and well-being of the environment and adjacent communities. 

By removing accumulated sediment on an annual maintenance schedule, the LA County Flood Control District can minimize the need for any emergency clean-out efforts.

Last year, LA Public Works removed around 25,000 cubic yards of sediment from during a six-week operation. This year, the county plans to limit the number of truck trips to 300 per day and avoid working on weekends, holidays, or during major events at the Rose Bowl Stadium nearby. 

Hauling operations will be conducted from 7 a.m. to 3 p.m., while work within the reservoir may continue until 6 p.m.

The Hahamongna Watershed Park perimeter trail will remain open to the public during the maintenance work. 

LA County encourages residents and visitors to stay informed and follow safety guidelines while enjoying the park. 

To learn more about the project, visit www.pw.lacounty.gov/swe/devilsgate or contact devilsgate@dpw.lacounty.gov.